Blood clot filters are typically used in conjunction with thrombolytic agents and anti-coagulants to treat pulmonary embolism occurring within a patient. These devices are generally implanted within a vessel such as the inferior vena cava, and function by capturing blood clots (emboli) contained in the blood stream before they can reach the lungs and cause permanent damage to the body. To filter emboli, many conventional blood clot filters utilize a number of independent filter legs coupled to an apical head that can be expanded within the body to form a conical-shaped surface that collects the emboli without disturbing the flow of blood. Once collected, a natural clot lysing process occurs within the body to dissolve the emboli collected by the filter.
Delivery of the blood clot filter within the body is generally accomplished via an introducer sheath percutaneously inserted through the femoral (groin) or jugular (neck) veins. Such introducer sheaths are generally tubular in shape, and include an inner lumen configured to transport the filter in a collapsed position through the body. Once transported to a desired location within the body, the filter can then be removed from within the introducer sheath, allowing the filter legs to spring open and engage the vessel wall. A needle, hook, barb, prong, wedge or other attachment means disposed on the base of each filter leg can be used to secure the filter within the vessel.
The filter legs exert an expansile force, directed radially outward against the vessel wall. Particularly in thinner walled vessels, prolonged application of such expansile forces on a relative small surface area on the vessel wall can lead to undesirable tissue movements, such as the hooks migrating through the vessel wall. When a particular filter, such as a vena cava filter, is to be removed, the radial expansion forces and resulting tissue changes may make the filter removal difficult.
Accordingly, there exists a need for improved filter anchoring that can avoid complications, trauma and removal difficulties related to continued strong expansion forces.